Advanced automotive, aircraft and other industrial equipment require lubricating oils that are effective at elevated temperatures. Polyesters, polyolefins, polyglycols, polyphenyl ethers, phosphates, silicones, etc. have been used as suitable lubricating oils. These lubricating oils undergo oxidative degradation at elevated temperatures. Loss of lubricating properties due to oxidative breakdown of these oils may cause failure of a part, or parts, in contact with the oils. The prior art discloses the stabilization of lubricating oils using various amines including diphenyl- and substituted diphenylamines, p-phenylenediamine and substituted naphthylamine. There appears to be no recognition of the use of secondary amines wherein one of the groups attached the amino nitrogen is an aromatic or substituted aromatic ring and the other group is an aliphatic carbon which in turn is attached to an aromatic or substituted aromatic ring.
U.S. Pat. No. 1,469,245 discloses N-(o-Hydroxybenzyl)-N'-phenyl-p-phenylene diamine as an anti-degradant for rubber. This compound belongs to the class of phenylene diamines which are known antioxidants. Furthermore, its use as a stabilizer for lubricating oils is neither disclosed in that patent, nor elsewhere.
U.S. Pat. No. 2,108,147 teaches a method for preparing secondary and teritary amines including 1-anilino-1-phenylethane. Hickenbottom teaches a phenylamine compound designated as alpha-phenylethyl-p-toluidine; see Journal of the Chemical Society (1934) pages 319-322. Beilstein discloses a phenyl amine compound of the general formula ##STR1## wherein R can be phenyl; see Handbuch Der Organishen Chemie 4th Ed. Vol XII Pat. IV pages 2403-4. None of the aforegoing compounds are taught to be antioxidants.